diff --git a/Developer-guides.md b/Developer-guides.md
index 91b838c..de9192c 100644
--- a/Developer-guides.md
+++ b/Developer-guides.md
@@ -104,6 +104,12 @@ Disable notifications on `cp`, `mv`, `rm` completion, selection sync to system c
 
 Warning: Saved sessions may no longer be usable when the number of contexts is switched.
 
+#### Matching filters only 
+
+    make O_MATCHFLTR=1
+
+Discard filter key when there's no match.
+
 ## Static compilation
 
 Install the GPM development library and set the Makefile variable `O_STATIC`.